1. Field of the Technology
The present disclosure relates generally to mobile communication devices or terminals which communicate in wireless communication networks, especially mobile terminals which communicate in both wireless local area networks (WLANs) such as IEEE 802.11-based networks, and wireless wide area networks (WWANs) such as cellular telecommunication networks.
2. Description of the Related Art
A mobile communication device or terminal may be designed to operate on two different types of heterogeneous wireless networks, such as a wireless local area network (WLAN) (e.g. IEEE 802.11-based wireless network) and a wireless wide area network (WWAN) (e.g. a cellular telecommunications network). Two different wireless transceiver portions of the mobile terminal are utilized for communications in the WLAN and WWAN.
The mobile terminal may switch communication operations between the WLAN and the WWAN (“vertical handoff”) during a voice or data call. The vertical handoff may involve, for example, a handover of a Voice over IP (VoIP) call in the WLAN to a circuit-switched voice call in the WWAN (e.g. GSM network). Acceptable solutions to a “seamless” handover may involve complex processing at several different layers of the Open Systems Interconnect (OSI) model. One particular concern involves the determination of the timing on when to handoff from one technology to another technology, i.e. to predict when the mobile terminal is leaving the coverage of one technology and entering into another. Handing over the call too early results in underutilization of the coverage a network access technology offers, and may undesirably result in “ping-ponging” between two access networks. On the other hand, handing over too late results in call drops and hence a poor user experience. The handover timing is particularly significant for voice calls in a WLAN, as WLAN coverage is short in range and is operating in a frequency band where traffic is highly dynamic and subject to high interference. Algorithms which maintain voice calls in the WLAN when conditions are acceptable would provide a good user experience and would help offload WWAN load by fully utilizing WLAN resources.
Accordingly, what are needed are methods and apparatus to improve mobile terminal transitioning between a WLAN and a WWAN, or other similarly situated wireless networks.